Developmental Analysis of aMedicago truncatula smooth leaf margin1Mutant Reveals Context-Dependent Effects on Compound Leaf Development  

Abstract

Compound leaf development requires highly regulated cell proliferation, differentiation, and expansion patterns. We identified loss-of-function alleles at the SMOOTH LEAF MARGIN1 (SLM1) locus in Medicago truncatula, a model legume species with trifoliate adult leaves. SLM1 encodes an auxin efflux carrier protein and is the ortholog of Arabidopsis thaliana PIN-FORMED1 (PIN1). Auxin distribution is impaired in the slm1 mutant, resulting in pleiotropic phenotypes in different organs. The most striking change in slm1 is the increase in the number of terminal leaflets and a simultaneous reduction in the number of lateral leaflets, accompanied by reduced expression of SINGLE LEAFLET1 (SGL1), an ortholog of LEAFY. Characterization of the mutant indicates that distinct developmental domains exist in the formation of terminal and lateral leaflets. In contrast with the pinnate compound leaves in the wild type, the slm1 sgl1 double mutant shows nonpeltately palmate leaves, suggesting that the terminal leaflet primordium in M. truncatula has a unique developmental mechanism. Further investigations on the development of leaf serrations reveal different ontogenies between distal serration and marginal serration formation as well as between serration and leaflet formation. These data suggest that regulation of the elaboration of compound leaves and serrations is context dependent and tightly correlated with the auxin/SLM1 module in M. truncatula.

Leaf development and morphogenesis

“…Interestingly, in M. truncatula, leaves of the MtPIN10/SLM1 (the Medicago PIN1 ortholog) mutant exhibit increased complexity and decreased marginal patterning, suggesting a more complex effect of auxin on leaf patterning in Medicago. However, the increased complexity might result from fusion of several leaves (Peng and Chen, 2011;Zhou et al, 2011).…”

The Root Hair “Infectome” of Medicago truncatula Uncovers Changes in Cell Cycle Genes and Reveals a Requirement for Auxin Signaling in Rhizobial Infection

“…To investigate the location of auxin signaling during infection, we used M. truncatula stably transformed with the auxin reporter DR5:GUS (Zhou et al, 2011) and observed that S. meliloti induced DR5:GUS in both infected and uninfected root hairs over the entire infection zone (root hair differentiation zone) 3 and 5 dpi ( Figures 7A and 7B). This increase in auxin signaling is consistent with the observation that auxin signaling is initially downregulated and then increases at the site of inoculation (Mathesius et al, 1998).…”

“…The primers used are listed in Supplemental Table 1 (Primers). The DR5:GUS analysis was performed in the R108 background using a stably transformed line (Zhou et al, 2011;Guan et al, 2013).…”

TheTrans-Acting Short Interfering RNA3 Pathway and NO APICAL MERISTEM Antagonistically Regulate Leaf Margin Development and Lateral Organ Separation, as Revealed by Analysis of anargonaute7/lobed leaflet1Mutant inMedicago truncatula

“…The formation of marginal serration tips is tightly correlated with auxin activity maxima, and the formation of lateral veins is defined by internalizing auxin through the center of the serrations. Perturbation of auxin transport by 1-N-naphthylphthalamic acid results in smooth leaf margins (DeMason and Chawla, 2004;Hay et al, 2006;Barkoulas et al, 2008;Zhou et al, 2011a). The second process is the repression of growth at the sinus by CUP-SHAPED COTYLEDON2 (CUC2).…”

“…In the model legume Medicago truncatula, the orthologs of Arabidopsis PIN1 and CUC have been identified and named SMOOTH LEAF MARGIN1 (SLM1) and NO APICAL MERISTEM (NAM), respectively (Zhou et al, 2011a;Cheng et al, 2012). The slm1 mutant exhibits a smooth leaf margin as a result of diffuse auxin distribution, suggesting the conserved roles of the auxin/SLM1 module in different plant species (DeMason and Chawla, 2004;Barkoulas et al, 2008;Koenig et al, 2009;Zhou et al, 2011a). In addition, the loss of function of SLM1 or NAM in M. truncatula leads to defects in the separation of lateral organs, indicating that both of them are positively correlated with the promotion of organ boundaries.…”